Manufacture of electrical contact materials

ABSTRACT

An electrical contact having high electrical conductivity, high hardness and strength capable of providing excellent arc erosion and low heat rise capability is obtained by blending a refractory metal powder and another metal powder, sintering the blend to at least 95% of its maximum theoretical density, finely dividing the sintered material such that the particle size is in the range of about 4-10 microns and there are no agglomerates larger than a Tyler mesh size of 200, compacting the finely divided material and sintering the resulting compact.

United States Patent 1191 1111 3,859,087

Backstrom Jan. 7, 1975 MANUFACTURE OF ELECTRICAL CONTACT MATERIALS Primary Examiner-Stephen J. Lechert, Jr. Assistant Examiner-R. E. Schafer [75] Inventor. lglaelvln L. Backstrom, Murrysville, Attorney Agent, or Firm ostrolenk, Faber Garb &

Soffen [73] Assignee: GTE Sylvania Incorporated,

Waltham, Mass. [57] ABSTRACT [22] Fled: 1973 An electrical contact having high electrical conductiv [21] APPL 323 71 ity, high hardness and strength capable of providing excellent arc erosion and low heat rise capability is obtained by blending a refractory metal powder and [52] US. Cl 75/213, 29/182, 75/221, another metal powder, Sintering the blend to at least 252/512 252/513 252/514 252/515 95% of its maximum theoretical density, finely divid- [51] Int. Cl BZZf 3/00, C226 1/04 ing the Sintered material Such that the particle Size is [58] Field of Search 75/221, 213; 29/182; in the range of about microns and there are no 252/512515 agglomerates larger than a Tyler mesh size of 200, compacting the finely divided material and sintering [56] References C'ted the resulting compact.

UNITED STATES PATENTS 6 Cl 2 D 2,179,960 11/1939 Schwarzkopf 75/221 x rawmg BACKGROUND OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the first step of the preferred em- Conventional processes for prod cing l i l 5 bodiment of this invention, a refractory metal powder ture above the melting point of the noble metal to obl tain the desired final integrity. When either of these methods of manufacture is used, the matrix is the refractory metal with the noble metal providing the filler material. However, because of the manufacturing method and the fineness of the materials used, a completely contiguous pattern of the filler material is extremely difficult to obtain.

I have discovered that if pre-blended finely divided powders are sintered to their maximum density and subsequently reduced to extremely finely divided powders and further compacted and sintered, a contiguous matrix of noble metal exists in a much more uniform condition than is possible by the aforementioned methods.

Heretofore, some methods have been proposed which include among their myriad steps sintering a mixture of metal powders, comminuting the sintered mixture, compacting the resulting material and sintering again. See, for example, U.S. Pat. Nos. 2,315,876; 2,205,611; and 1,812,811. In such procedures, however, the initial sintering step is employed for the purpose of imparting a degree of integrity to the mixture as an aid in subsequent handling such as shaping and the like. Since a fully sintered material is very difficult to shape by cutting, grinding and the like, such prior art procedures sintered only to the extent of obtaining the desired integrity and did not approach the maximum theoretical density of the blend. 1 have found that when the initial sintering is to the extent of at least 95% the maximum theoretical density and the sintered material is thereafter comminuted to a particular particle size, an electrical contact can be obtained which is superior to the prior art materials.

It is the object of this invention to provide a superior performing electrical contact which has high electrical conductivity, high hardness and strength capable of providing excellent arc erosion and low heat rise capability and to provide a process for the manufacture of such contacts. This and other objects of the invention will become apparent to those skilled in the art from the following detailed description.

SUMMARY OF THE INVENTION This invention relates to a superior performing electrical contact and the method of manufacturing such contact. More particularly, the invention relates to a superior performing electrical contact which is manufactured by blending a refractory metal powder and another metal powder, sintering the blend to at least 95% of its maximum theoretical density, finely dividing the sintered material such that the particle size is in the range of about 4-10 microns and there are no agglomerates larger than a Tyler mesh size of 200, compacting the finely divided material and sintering the resulting compact.

and a noble metal powder are blended together. The powders are preferably employed in the most highly divided state available in order to obtain the greatest intimacy of the mixture. Preferably, the powders are finer 0 than a Tyler mesh size of 325 (about 39 microns maxi mum). The blending and mixing can be accomplished by any of the procedures and with any ofthe equipment known in the artas, for example, in a double cone blender, ball mill, tumbling mixer and the like.

The blended powders will generally comprise about 4095 weight percent refractory metal with the balance essentially being a metal of groups 1B, llB and/or VIII, preferably copper or a noble metal such as gold or silver. Of course, more than one refractory metal and/or noble metal can be used. Typical of the refractory metals blended with the noble metal are tungsten, molybdenum, tantalum, niobium, titanium, zirconium and vanadium from groups lVB, VB and VIB of the Periodic Table.

The blended powders are then sintered. The mechanics of a sintering step are well known in the art and do not form a part of this invention. In general, a temperature of about 850l200 C. for about 0.5 hour and a protective atmosphere excluding reaction with oxygen is used. It is necessary, however, in order to obtain the superior characteristics of the electrical contact of this invention that the blended materials be fully sintered. In other words, in order to accomplish the objectives of this invention, it is necessary to sinter the blend until at least 95%, preferably at least 98%, of its maximum theoretical density is obtained.

The fully sintered material is thereafter comminuted into an extremely finely divided powder. It is important that substantially all of the resulting powder particles have a size in the range of about 4l0 microns and that any agglomerates which may be present are smaller than a Tyler mesh size of 200 (about microns maxi mum). The 4 micron size is essentially dictated by the capabilities of the commercially available processes for finely dividing fully sintered materials. If the particle sizes are greater than 10 microns, it is difficult to obtain densification when the powder is pressed and sintered; the result is a sintered compact having a high degree of pores and the superior properties of the electrical contact of this invention are not obtained.

The comminuting can be accomplished by any of the procedures and in any of the apparatus known in the art. Examples of usable equipment and processes can be found in US. Pat. Nos. 3,184,169, 3,482,786, and

in copending application Ser. No. 246,591 filed Apr.

24, 1972, now abandoned.

In the final steps of the process of this invention, the finely divided powder is compacted, i.e., consolidated into the desired geometric shape, and sintered by processes heretofore known in the art. In general, the powder is placed in a mold and pressed by the application of about 30 t.s.i. pressure thereby obtaining a dense compact in the desired electrical contact shape. The compact is thereafter sintered to its maximum density to obtain the final product.

The following Examples are presented to further illustrate the invention but are not intended to limit it.

Unless otherwise specified, throughout this specification and claims, all temperatures are in degrees centigrade and all parts and percentages are by weight.

A mixture containing 65 weight percent tungsten powder and 35 weight percent silver powder were blended in a high velocity mixer for 3 minutes and the resulting blend was sintered to about 95% of its maximum theoretical density and then finely divided into a particle size of about 4l0 microns. The finely divided powder was passed through a Tyler mesh of 200 to separate any large particles from the powder. Thereafter the powder was placed in a mold, pressed under a pressure of 35 t.s.i. and the compact was sintered at 1060 C. for minutes to obtain the maximum density. Examination of the resulting part showed that there was a contiguous matrix of silver and a minimum of porosity was evident. The electrical conductivity of the part was 53% IACS, the hardness was 95R,, and the density was 98% of the minimum theoretical density. A photomicrograph at 400X of the contact is set forth in FIG. 1

As a comparison, a blend of 65 weight percent tungsten powder and 35 weight percent silver powder was compacted and sintered in the same manner as the final 2 steps described in the preceding paragraph. The resulting electrical contact had an electrical conductivity of 50% IACS, a hardness of 90R,, and a density of 97% of the minimum theoretical density. FIG. 2 is a photomicrograph at 400X of the contact.

Various changes can be made in the process and products of this invention without departing from the spirit and the scope thereof. The various embodiments presented herein were for the purpose of further illustrating the invention but were not intended to limit it.

I claim:

1. A process for obtaining an electrical contact having high electrical conductivity, high hardness and strength capable of providing excellent arc erosion and low heat rise capability which comprises blending at least one refractory metal powder with at least one powder of a metal from groups IB, IIB and VIII of the Periodic Table, sintering the blend to at least of its maximum theoretical density, finely dividing the sintered material such that the particle size is in the range of about 4-10 microns and there are no agglomerates larger than a Tyler mesh size of 200, compacting the finely divided material, and sintering the resulting compact.

2. The process of claim 1 wherein the refractory metal is from groups IVB, VB and VIB of the Periodic Table.

3. The process of claim 2 wherein the blend contains about 40-95 weight percent refractory metal.

4. The process of claim 3 wherein the metal of groups IB, [[8 and VIII is a noble metal.

5. The process of claim 4 wherein the refractory metal is tungsten and the noble metal is silver.

6. The process of claim 3 wherein the metal of groups IB, IIB and VIII is copper, gold or silver. 

2. The process of claim 1 wherein the refractory metal is from groups IVB, VB and VIB of the Periodic Table.
 3. The process of claim 2 wherein the blend contains about 40-95 weight percent refractory metal.
 4. The process of claim 3 wherein the metal of groups IB, IIB and VIII is a noble metal.
 5. The process of claim 4 wherein the refractory metal is tungsten and the noble metal is silver.
 6. The process of claim 3 wherein the metal of groups IB, IIB and VIII is copper, gold or silver. 